The present invention relates generally to light beam projectors including pendulous compensators and, more particularly, to apparatus for damping motion of a pendulous compensator to rapidly stabilize the light beam emanating from such a projector.
Light beam, typically laser beam, systems are used in leveling, squaring and other alignment and control functions in the building and construction industries. When using light beam systems, it is important to be able to position a light beam source or projector such that the light emitted by the projector is maintained in a desired orientation for example horizontal or at a selected angle relative to horizontal. Since stable horizontal leveling of the projector may be difficult, particularly at a construction site, prior art light beam projectors have employed pendulous compensators to direct a vertically emanating light beam in a desired horizontal direction regardless of whether the projector is tilted and hence not absolutely horizontal.
A simplified schematic diagram of a laser beam projector 100 including a housing 102, a laser beam source 104, focusing lenses 106 and a conventional pendulous compensator 108 is shown in FIG. 1. The pendulous compensator 108 is shown as being mounted to a bracket 110 and comprising a pendulum arm 112 pivotally coupled to and suspended downwardly from the bracket 110 for pivotal movement within a plane perpendicular to a pivot axis 114 of the arm 112, and a beam reflecting mirror 116 fixedly attached to the lower end of the arm 112. The laser beam source 104 and the bracket 110 are fixedly attached to the housing 102 and aligned such that a laser beam 118 projected upwardly from the laser beam source 104 lies within the pivot plane of the arm 112 and preferably passes through the pivotal axis 114 of the pendulum arm 112 if the arm 112 and beam reflecting mirror 116 are removed.
When the projector 100 is placed in a true horizontal orientation, the laser beam 118 is emitted in a true vertical orientation and the pendulum arm 112, which in theory due to gravity always assumes a true vertical orientation, is aligned with the laser beam 118. The laser beam 118, which is first focused and collimated by the lenses 106, is reflected by the mirror 116 in the horizontal direction within the pivot plane of the pendulum arm 112. If the laser beam projector 100 becomes tilted away from horizontal, such tilting is compensated by the movement of the pendulum arm 112. However, if the pendulum arm 112 is freely movable about the axis 114, compensation errors result. Accordingly, a pair of counterbalancing springs 120 may be connected between the pendulum arm 112 and the housing 102 to correct the errors which would be created by true pendulous motion of the arm 112.
As seen in FIG. 2, the housing 102 and hence the laser beam 118 are oriented at an angle "a" relative to vertical. However, the pendulum arm 112 biased by the springs 120 is now displaced counterclockwise about the axis 114 from the line of emergence of the laser beam 118 through an angle "a/2" which compensates for the angular tilt of the housing 102. In accordance with known operating principles of the pendulous compensator 108, the laser beam 118 continues to be reflected by the mirror 116 in the horizontal direction. As an alternative to the counterbalancing springs 120, the pendulum arm 112 can be cantilevered or fixedly mounted to the housing 102 with the arm 112 formed such that it bends or deflects to compensate for tilting movement of the projector 100.
The operation of a pendulous compensator as just described is satisfactory if the projector incorporating the compensator is not subject to vibrations and can tolerate substantial stabilization times whenever the projector is initially positioned or moved. However, errors arise from oscillations of the pendulum arm due to vibrations which commonly occur in building and construction environments, and extended settling or stabilization times are a source of frustration and cost time and money.
Pneumatic and eddy current motion damping arrangements have been used in the past in an attempt to nullify vibrations and reduce settling times. For example, see U.S. Pat. No. 4,679,937 which issued to Gary Cain et al on July 14, 1987 and is assigned to the same assignee as the present invention. Unfortunately, both arrangements have various drawbacks. In the case of pneumatic damping, temperature variations can produce substantial errors or require complicated and not totally effective compensation arrangements. Further, pneumatic damping arrangements are somewhat difficult to adjust to provide the required damping and oftentimes over or under damping of the pendulous compensator result. Previous attempts at eddy current damping for pendulous compensators have not proven to be very effective for low velocity damping and would not permit operation of the pendulous compensator over an extended range of tilt angles.
Accordingly, there is a need for an improved damping arrangement for pendulous compensators used in light beam projectors which can effectively damp motion in a pendulous compensator over a substantial temperature range and an extended range of tilt angles of the light beam projectors.